It is well-known that when ferrous metals are exposed to water and corrode that hydrogen atoms are liberated at a rate corresponding to the rate of corrosion activity as a result of the dissociation of water molecules into hydrogen atoms and hydroxyl groups. Some of these hydrogen atoms permeate and migrate through the ferrous metal body. When such atoms resurface they combine to form molecular hydrogen gas and then dissipate.
Various systems have sought to exploit the solubility and dissipation of atomic hydrogen as a means of monitoring the corresponding magnitude of corrosion activity.
U.S. Pat. No. 5,279,169, issued Jan. 18, 1994, and U.S. Pat. No. 5,392,661, issued Feb. 28, 1995, to H. Bruce Freeman, and references cited therein relate to methods for monitoring the magnitude of corrosion occurring at a surface of a ferrous metal body when exposed to a corrosive material, such as water.
Solid phase welding is a method of welding metals by the application of pressure so as to produce interfacial plastic deformation of the metals at the interfacial surfaces which breaks up the contaminant surface films to expose virgin contact surfaces for bonding.
A solid phase weld may be achieved by a process identified as "impact welding" which consists of driving or propelling one metal layer against another metal layer at a sufficient velocity and at an oblique impact so as to cause bonding of the two metal layers together at the common interfacial region of contact. Impact Welding has been achieved by those skilled in the art by utilizing magnetic propulsion equipment, gas guns and explosives to propel the metal layers together. If the metals are driven together by means of explosion, the process is known as explosion welding. Reference is made to U.S. Pat. No. 4,747,350, issued May 31, 1988, and U.S. Pat. No. 4,842,182, issued Jun. 27, 1989, to Alexander Szecket, for a further explanation.
In explosion welding, metal plates or layers which are to be welded are spaced apart relative to one another in either generally parallel relation or inclined relation and a layer of suitable explosive charge disposed on one of the metal layers is detonated so as to impart kinetic energy to the "flyer" plate causing the flyer plate to collide obliquely with the stationary "parent" plate. The explosive, while detonating, produces a force normal to the flyer plate causing the flyer plate to impact the parent plate obliquely at a collision or impact angle. As the detonation proceeds along the flyer plate, it progressively drives the flyer plate along the parent plate at a particular welding velocity. If two metal layers are to be bonded the explosive charge may be disposed on both metal layers.
U.S. Pat. Nos. 3,728,780 and 3,137,937 generally relate to explosion welding, which may be utilized to weld different metals together.
U.S. Pat. No. 3,813,758 teaches that a metal jet is formed at the point of impact between the flyer plate and parent plate. It is believed that this jet which contains the contaminant surface layers of both plates is forced outwardly at a high velocity during the explosion welding process. This cleaning operation allows a solid phase weld to be formed between the interfacial clean metallic surfaces of the plates under the intense local pressure in the region of contact.
U.S. Pat. No. 3,583,062 discloses that three types of bonded zones may result from explosion welding, viz;
(a) a direct metal to metal bond (with a straight interface); PA0 (b) a uniform melted layer in which the metals are bonded together with an intervening layer of solidified melt substantially homogeneous composition; and PA0 (c) a wavy type of bond zone comprised of periodically spaced discreet regions of solidified melt, between areas of direct metal to metal bond. PA0 (a) Perimetrical explosive bonding differs from cladding in the collision mechanism and in the explosives used. The collision mechanism in cladding takes place in the direction of detonation, whereas in perimetrical bonding it occurs at 60-70 degrees to that direction at both sides of the pathway of detonation to provide a "double zipper" effect. PA0 (b) Perimetrical explosion bonding differs from seam and lap welding in the nature of the high detonation explosives used and the use of a "V" shaped groove or equivalent arrangement for a stand-off uniformity and subsonic collision--an essential requirement for jet formation. Explosive cladding requires low detonation velocity explosives (1700-3700 m/s), while explosive seam or lap welding use an RDX high detonation velocity lead sheathed ribbon (8600 m/s). The high detonation velocity of use in the present invention comes from e.g. a PETN strip (6800 m/s) that is not lead-sheathed, and, thus does not present upon detonation, an environmental disadvantage.
Moreover, U.S. Pat. No. 3,397,444 generally teaches that products having the wavy type bond interface are preferred in many situations because of their normally higher strength, and defines values of parameters such as collision velocity so as to produce the preferred wavy interface.
Similarly, U.S. Pat. No. 3,583,062 states that the wavy bond zone is preferred over the substantially straight bond because of the larger interfacial area the wavy bond provides, and also defines the value of certain parameters which will produce the preferred wavy interface.
However for metal combinations tending to form brittle intermetallics, the melt associated with the bonded wavy interface presents zones of weakness. Metal combinations which tend to form brittle combinations are well known to those skilled in the art and generally encompass those metal combinations which have a wide dissimilarity between the densities of the metals to be bonded, which include for example, aluminum to steel, aluminum to copper, zirconium to steel, tantalum to steel, titanium to steel, titanium to copper, and their respective alloys.
Brittle intermetallics are diffusion products, and are undesirable, particularly when the welded zone is subjected to an increase in temperature which enhances diffusion.
Aforesaid U.S. Pat. Nos. 5,279,169 and 5,392,661 describe in broad aspects a corrosion monitor for monitoring the corrosion of a non-porous steel body by measuring the diffusion of hydrogen atoms through a selected area of the body from a second surface to an opposite first surface thereof, comprising:
(a) a chamber-defining member; PA1 (b) seal means extending around the marginal perimeter of the chamber-defining member for sealably securing the chamber-defining member to the first surface so as to define with said selected area of the first surface of the non-porous steel body a sealed chamber which is impervious to the flow of gas or liquid; PA1 (c) said chamber defining member being adapted to closely conform to the surface shape of said selected area and to lie in close proximity thereto, said chamber defining member comprising an element which is sufficiently flexible that it deflects toward, and comes to rest upon, the first surface of the body upon evacuation of the chamber so as to reduce the volume of the chamber and define a fixed interstitial volume of the chamber throughout an optimal vacuum pressure operating range; PA1 (d) means for connecting an evacuating means to the chamber defining member to permit substantial evacuation of the contents of the chamber to establish a partial vacuum therein; PA1 (e) means for isolating the chamber from the evacuation means after the partial vacuum has been established to maintain the partial vacuum in the chamber so that hydrogen atoms that are generated as a result of corrosion of the second surface of the body and which diffuse through the non-porous material of the body and which exit the first surface within the chamber and which combine to form hydrogen molecules, collect in the chamber thus resulting in a decay of the vacuum in the chamber; and PA1 (f) vacuum monitoring means for monitoring the decay of the vacuum in the chamber over time to give an indication of the rate of diffusion of hydrogen atoms through the selected area of the non-porous steel body and hence an indication of the rate of corrosion of said second surface. PA1 (a) positioning said second portion and said second metal in generally spaced apart parallel relation; PA1 (b) propelling said first portion into collision with said second metal so as to produce said hermetically sealed bond between said first portion and said second metal. PA1 (a) positioning said second portion and said second metal in generally spaced apart parallel relation; PA1 (b) applying a layer of high velocity explosive charge having a velocity selected from 5,500-9,000 m/s upon said first portion; PA1 (c) detonating said explosive charge so as to propel said first portion into collision with said second metal so as to produce said hermetically sealed bond between said first portion and said second metal. PA1 (a) positioning said second portion and said second metal in generally spaced apart relation; PA1 (b) propelling said first portion into collision with said second metal so as to produce said hermetically sealed envelope or chamber between said first portion and said second metal. PA1 (a) a chamber-defining member; PA1 (b) seal means extending around the marginal perimeter of the chamber-defining member for sealably securing the chamber-defining member to the first surface so as to define with said selected area of the first surface of the non-porous steel body a sealed chamber which is impervious to the flow of gas or liquid; PA1 (c) said chamber defining member being adapted to closely conform to the surface shape of said selected area and to lie in close proximity thereto, said chamber defining member comprising an element which is sufficiently flexible that it deflects toward, and comes to rest upon, the first surface of the body upon evacuation of the chamber so as to reduce the volume of the chamber and define a fixed interstitial volume of the chamber throughout an optimal vacuum pressure operating range; PA1 (d) means for connecting an evacuating means to the chamber defining member to permit substantial evacuation of the contents of the chamber to establish a partial vacuum therein; PA1 (e) means for isolating the chamber from the evacuation means after the partial vacuum has been established to maintain the partial vacuum in the chamber so that hydrogen atoms that are generated as a result of corrosion of the second surface of the body and which diffuse through the non-porous material of the body and which exit the first surface within the chamber and which combine to form hydrogen molecules, collect in the chamber thus resulting in a decay of the vacuum in the chamber; and PA1 (f) vacuum monitoring means for monitoring the decay of the vacuum in the chamber over time to give an indication of the rate of diffusion of hydrogen atoms through the selected area of the non-porous steel body and hence an indication of the rate of corrosion of said second surface; PA1 the improvement comprising wherein said chamber-defining member has a first portion having a high energy contoured hermetic seal with said first surface of said body made by a method as hereinabove defined. PA1 (a) a chamber-defining member; PA1 (b) a steel body in which at least said selected area is impervious to the flow of gases or liquids; PA1 (c) seal means extending around the marginal perimeter of the chamber-defining member for sealably securing the chamber-defining member to the first surface so as to define with said selected area of the first surface of the body a sealed chamber which is impervious to the flow of gases or liquids; PA1 (d) said chamber defining member being adapted to conform closely to the surface shape of said selected area of the first surface so as to lie in close proximity thereto to minimize the volume of the sealed chamber defined between the selected area of the first surface and the chamber-defining member; PA1 (e) means for connecting an evacuating means to the chamber defining member to permit substantial evacuation of the contents of the chamber to establish a partial vacuum therein; PA1 (f) valve means for isolating the chamber from the evacuation means after the partial vacuum has been established to maintain the partial vacuum in the chamber so that hydrogen atoms that are generated as a result of corrosion of the second surface of the body and which diffuse through the material of the body and which exit the first surface within the chamber and which combine to form hydrogen gas molecules, collect in the chamber thus resulting in a decay of the vacuum in the chamber; and PA1 (g) vacuum monitoring means for monitoring the decay of the vacuum in the chamber over time to give an indication of the rate of diffusion of hydrogen atoms through the material of the body and hence an indication of the rate of corrosion of said second surface; PA1 the improvement comprising wherein said chamber defining member has a first portion having a high energy contoured hermetic seal with said first surface of said body made by a method as hereinabove defined.
However, it is known that applications that require a precisely defined sealed space particularly between dissimilar metals are limited by the means by which the two metals may be attached.
In the case of applications such as disclosed in aforesaid U.S. Pat. Nos. 5,279,169 and 5,392,661 having specific vacuum requirements, for example, an epoxy resin is used to attach, for example, a 0.1 mm thickness stainless steel foil to a cylindrical carbon steel pipe of requisite dimension. Unfortunately, this method of attachment is temporary and does not provide a reliable seal particularly under extreme cold weather conditions and temperature fluctuations. Further, in some circumstances, the resins used may produce harmful vapors that may preclude their use entirely.
In the case of pressure containment requirements, welding alternatives, such as fusion or arc welding, or any temperature related bonding technologies create heat affected zones in the underlying metallic structure and, thereby, introduce metallurgical weaknesses which may damage the metal in such a way as to make the welding alternative impossible.
In the case of impact bonding produced either by explosives, compressed gas or electromagnetic discharge, a high pressure low temperature contact is created between a planar flyer plate and a planar base plate such that the two surfaces meet at a precise angle and velocity and a metallurgical bond is achieved between them.
However, there remains a need to provide a suitable metallurgical bond between metals which is sufficiently hermetic as to, for example, provide a satisfactory product as required in the apparatus and utility described in aforesaid U.S. Pat. Nos. 5,279,169 and 5,392,661 in the determination of the magnitude of corrosion at the surface of a ferrous metal body.